Dr Delbridge has told the royal commission that two senior Environment Department officials told him safety was not a concern.

"Mr [William] Kimber was prepared to accept that there could be injuries, serious injuries," Dr Delbridge said.

"The program policy was that was acceptable because the responsibility was to be pushed out to the installers."

Dr Delbridge told the royal commission that was, for want of a better term, the party line.

"And that's what I had concerns with - for the HIP program not to be regulating, not to get involved in the safety aspect," he said.

Dr Delbridge gave evidence last week that he was verbally threatened when he raised safety concerns about the program.

He told the royal commission he did not mention specific safety concerns in emails to senior officials before his dismissal because he wanted to discuss them in person along with bullying claims.

'Scheme was flawed' says Commonwealth lawyer

Mr Howe admitted the insulation scheme had a number of flaws, but told the commission whistleblowers were not silenced.

"The Commonwealth will accept unquestionably that this program was afflicted with many many deficiencies and imperfections," he said.

"But I anticipate that the Commonwealth will be putting submissions that the Commissioner ought regard this evidence - this witness's evidence about what I've just described - as either unreliable or untruthful."

However, senior South Australian public servant Rodney Hook Royal today told the Commission installer licensing measures in his state were seen as an impediment to the roll-out of the scheme.

Mr Hook says South Australia was the only jurisdiction at the time requiring installers be trained and licensed.

"The Commonwealth intent in the program was to roll it out quickly, runs on the board, it had an employment agenda," he said.

"What we were saying to the Commonwealth was all well and good, but we have a requirement for licensing and that required training and so forth."

The Abbott Government established the royal commission in December and charged it with finding out whether the former Labor government was given any advice, warnings or recommendations about the program.

The royal commission will also investigate how advice, warnings and recommendations were identified, assessed and managed.

During the HIP rollout, hundreds of house fires broke out, many of them in ceilings where foil insulation had been incorrectly installed.